This project has focused on the metabolic trafficking which takes place between neurons and astroglial cells and is an important part of the reciprocal relationship which has been shown to exist between these two cell types. The substrates, which neurons need in order to function, are both those which 1) can be used for energy production and 2) those which can serve an anaplerotic role i.e. four and five carbon intermediates, which can replace the citric acid cycle intermediates lost when the neurotransmitters, glutamate and GABA are released from the neuron into the extracellular space. The studies which we have carried out have addressed the problem of how the astroglial cells may function in supplying the nutritive needs of the surrounding neurons. Both CO2 fixation and glucose metabolism appear to play an important role in this process. Since the "metabolic trafficking" which occurs between neurons and astroglial cells implys a two-way process, we have also been interested in studying the ways in which neurons may signal the astroglial cells and thereby influence the production and release of products into the extracellular space. These products would then be available to the surrounding neurons. We have found that the potassium, which is released into the extracellular space when neurons are stimulated, is an important factor in regulating both the production and release of products from the astroglial cells and may regulate the uptake of these products by the surrounding neurons.